U.S. Reissue Pat. No. USRE39593 discloses a variety of 1-phenyl-3-dimethylaminopropane compounds, processes for their preparation, pharmaceutical compositions comprising the compounds, and method of use thereof. These compounds have the utility as analgesic active ingredients in pharmaceutical compositions. Among them, tapentadol hydrochloride, 3-[(1R,2R)-3-(dimethylamino)-1-ethyl-2-methylpropyl]phenol hydrochloride, is a centrally-acting analgesic with a unique dual mode of action as an agonist at the μ-opioid receptor and as a norepinephrine reuptake inhibitor. Tapentadol hydrochloride is represented by the following structural formula:

Various processes for the preparation of tapentadol, its enantiomers and related compounds, and their pharmaceutically acceptable salts are disclosed in U.S. Pat. Nos. 6,248,737 and 6,344,558; and PCT Publication Nos. WO 2004/108658, WO 2005/000788, WO 2008/012046, WO 2008/012047 and WO 2008/012283.
U.S. Pat. No. 6,248,737 (herein after referred to as the '737 patent) discloses processes for the preparation of tapentadol or a pharmaceutically acceptable salt thereof. While the '737 patent mentions that some of the disclosed compounds can form salts with physiologically acceptable acids, for example, hydrochloric acid, hydrobromic acid, sulfuric acid, methanesulfonic acid, formic acid, acetic acid, oxalic acid, succinic acid, tartaric acid, mandelic acid, fumaric acid, lactic acid, citric acid, glutamic acid and/or aspartic acid, only the hydrochloride salt had been prepared and isolated.
According to the '737 patent, tapentadol is prepared by the reaction of (−)-(2S,3S)-1-dimethylamino-3-(3-methoxyphenyl)-2-methylpentan-3-ol hydrochloride with thionyl chloride to produce (−)-(2S,3S)-[3-chloro-3-(3-methoxyphenyl)-2-methylpentyl]-dimethylamine hydrochloride, followed by subsequent removal of the ‘Cl’ substituent by treatment with zinc borohydride, zinc cyanoborohydride or tin cyanoborohydride, to produce (−)-(2R,3R)-[3-(3-methoxyphenyl)-2-methylpentyl]-dimethylamine hydrochloride. The (−)-(2R,3R)-[3-(3-methoxy phenyl)-2-methylpentyl]-dimethylamine hydrochloride is then converted to (−)-(1R,2R)-3-(3-dimethylamino-1-ethyl-2-methylpropyl)-phenol (tapentadol) by reacting with concentrated hydrobromic acid at reflux.
U.S. Patent Application No. 2007/0213405 (hereinafter referred to as the '405 application) discloses two crystalline polymorphs (Form A & Form B) of (−)-(1R,2R)-3-(3-dimethylamino-1-ethyl-2-methylpropyl)-phenol hydrochloride (tapentadol hydrochloride), and characterizes them by powder X-ray diffraction (P-XRD), Infra Red spectroscopy (IR), RAMAN spectroscopy and crystal structure analysis. The '405 application further teaches that the procedure described in example 25 of U.S. Pat. Nos. 6,248,737 and 6,344,558 as well as EP 693475 B1 produces crystalline Form B of tapentadol hydrochloride.
U.S. Patent Application No. 2009/0149534 (hereinafter referred to as the '534 application) discloses three crystalline modifications (modifications A, B & C) of tapentadol base, processes for their preparation, and characterizes the modifications by powder X-ray diffraction (P-XRD) pattern and RAMAN spectroscopy.
There remains a need for novel solid state forms of tapentadol salts.